1. Field Of The Invention
This invention relates to an apparatus and an associated method for facilitating solids transport in a pneumatic conveying line.
2. Description Of The Prior Art
Pneumatic conveying lines employ gas to move solids through an enclosed pathway, usually a pipeline. A problem associated with the transport of certain solids by means of pneumatic conveying lines is particle degradation.
It has been known that reducing gas velocity creates more favorable conditions for solids transport. Low velocity conveying not only reduces particle degradation, but also results in lower power requirements.
One known method of reducing gas velocity is to increase the cross-sectional area of the pneumatic conveying line. "Stepped" pneumatic conveying lines abruptly increase in cross-sectional area at periodic intervals. Unfortunately, every increase in the cross-sectional area of the pneumatic conveying line also increases costs.
Another method of reducing gas velocity is to reduce the fluid flow rate. The present invention accomplishes this by purging gas from the pneumatic conveying line.
The method of drawing air out of a pneumatic conveying line has been used to perform several functions. U.S. Pat. No. 4,859,120 discloses a pneumatic conveying system. A stall device is interposed between the ejector and the outlet side of the transporting piping, and includes a suction portion, formed by providing a multiplicity of air vents on the transporting piping, and an exhaust fan. The exhaust fan is driven such that the exhaust air flow rate becomes higher than the flow rate of the conveying wind power from the ejector whereby atmosphere is allowed to flow into the suction portion from the outlet of the transporting pipe. The flow of this atmospheric wind becomes counter flow wind against the articles conveyed.
U.S. Pat. No. 4,083,607 discloses a gas transport system for powder. A delivery pipe has an end portion of porous material having a pore size smaller than the particles of the powder. The porous end portion is surrounded by a jacket in which a vacuum is drawn to draw off transport gas and reduce filter capacity which would otherwise be required to remove it.
U.S. Pat. No. 4,704,054 discloses a tobacco discharge unit for the hopper of a continuous-rod cigarette making machine. Air from a pneumatic conveying line passes through a screen separating upper and lower compartments of the unit and out an outlet in the upper compartment. Tobacco distributing means prevent excessive packing.
In spite of the foregoing known systems, there remains a need for a device which reduces particle degradation and power requirements in pneumatic conveying lines, which eliminates the need for stepped pneumatic conveying lines and which is economical and easy to retrofit into existing systems.